1. Field of the Invention
This invention relates generally to coupled washer-nut assemblies and, more particularly, to such assemblies in which the washer and nut are freely rotatable relative to one another.
2. Description of the Prior Art
A wide variety of coupled washer-nut assemblies are known in the prior art. Such assemblies have several recognized advantages over separate nuts and washers. For example, they are typically more convenient to handle and apply to a cooperating bolt, and simpler to package and ship, than separate nuts and washers. They also reduce the loss of washers to be used with nuts in given applications and effectively insure that the proper size and shape of washer is consistently available for each application.
In many of the earlier coupled washer-nut assemblies, the washer and nut were separately fabricated but non-rotatably coupled. A characteristic non-rotatably coupled, or fixed, washer-nut assembly is disclosed in U.S. Pat. No. 2,761,349. Fixed assemblies of this type are undesirable for use in many applications because of the relatively high torque that must be applied to the nut to achieve a desired degree of tension on a cooperating bolt. Since both the nut and the washer rotate together even after the washer is initially tightened against a confronting surface of a workpiece, excess torque must be applied to the nut to overcome frictional forces between the washer and the confronting surface. This excess torque increases as the tightness of the nut on the bolt is increased. Also, during tightening, the edge of the washer oftens scores, gouges or otherwise damages the confronting surface. Additionally, when a sealing element is disposed adjacent the undersurface of the washer, the coincident rotation of the washer often causes the element to be torn, ruptured or deformed and thereby rendered less effective.
Because of the above problems, most later-designed washer-nut assemblies coupled the washer and the nut so that both components could rotate independently of one another. Examples of such rotatably coupled, or free-spinning, assemblies are shown in the following references: U.S. Pat. Nos. 2,851,079; 2,943,661; 3,569,491; 3,796,123; and in British Pat. No. 929,807.
One of the primary objectives of such free-spinning assemblies is the reduction of the torque which must be applied to the nut to realize a specified degree of tension on the bolt onto which the nut is turned. Many of the free-spinning washer nut assembly designs have served only to delay the point at which the washer commences to rotate with the nut and relative to the confronting surface, and thus have been only partly successful in achieving the above objective. Other prior assemblies have been more effective in reducing washer rotation during tightening, but have been susceptible to loosening on the bolt after tightening due to the vibration or flexure of the workpiece. Such assemblies have thus been found to be undesirable for use in applications in which vibration and flexure of the workpiece are to be expected.
Still other prior assemblies, in order to reduce the likelihood of washer rotation during tightening and to provide an increased resistance to loosening after tightening on a bolt, have required relatively complex washer and nut constructions and designs. As a result, these latter assemblies have been relatively difficult and expensive to produce.